Wire or rod (hereinafter termed "wire" only) is formed at high speed in a rolling or drawing mill and is delivered in straight condition to a coiler that forms it into a succession of large-diameter turns that it deposits on a surface, normally a conveyor of some type. Thence the coiled wire is moved through subsequent treatment steps such as heat treatment, descaling, pickling, or simply cooling. It is critical that the wire be deposited in uniformly shaped and spaced coils so that the subsequent treatment stage is effective.
The typical coiling system comprises a so-called laying tube twisted in three dimensions and having an upstream end opening axially in line with an axis about which the tube is rotated and a downstream end which opens at a location radially offset from the axis and is directed generally tangentially. The straight wire is fed into the upstream end of the laying tube as it is rotated about its axis so that as the wire passes through the tube it is bent into an arcuate shape and will fall in a coil when leaving the downstream end of the tube.
Two main factors influence the operation of the coiler, wire diameter and wire speed. As wire diameter increases the friction inside the tube increases, creating substantial drag on the wire. As speed increases the wire is urged with greater centrifugal force against the inside wall of the tube so that once again friction inside the tube increases along with drag on the wire. Normally wire speed is, however, inversely related to wire diameter with thick wire moving much more slowly than thin wire. It is therefore standard to provide a drive engaging the rod just upstream of the upstream end of the laying tube to accelerate the trailing ends of thick wires and slow the trailing ends of thin wires, which may move at 100 m/sec.
The incoming workpiece is not endless and a problem occurs as the trailing end of a wire workpiece passes through the coiler. Due to the lack of upstream drag such a trailing end is likely to whip through the tube and not be sufficiently formed, that is to be laid on the conveyor in turns that are of excessive diameter. This can cause substantial problems so that frequently this section is cut away and must be recycled.
It has been suggested in German patent document 1,814,280 of G. Bollig to provide a bending roller at the downstream end of the laying tube which presses the exiting wire against the inner surface of a stationary laying drum coaxially surrounding the laying tube. This ensures accurate forming of like-diameter turns but represents extra equipment subject to substantial wear.
Old East German patent 229,314 of N. Brennecke proposes a complex control system that controls the rotation rate of the laying tube and the advance rate of the wire drive while monitoring the position of the wire end so that like-diameter turns are produced right to the trailing end of the wire. While relatively effective, this system is quite complex and not easily retrofitted to an existing wire mill.